Vulcanizing rubber



UNETED srarss PATENT oFFIcs No Drawing. ApplicationJuly 16, 1923 Serial No. 651,968

15 Claims. (Cl. 18-53) This invention relates to improvements in the use of organic, nitrogeneous, substances that assist in or accelerate the vulcanization of rubber, and has for its object-the utilization of new reac- 5 'tions and products to this'end.

This specification forms a continuation in part of an application filed July 30, 1920 as Ser. No. 399,979 and issued in part Aug. 21, 1923 as No. 1,465,743 andbrings forward products disclosed in the earlier specification as originally filed, but which were not printed in the patent that finally issued.

This specification is also a continuation in part of Ser. No, 647,765 filed June 25, 1923, wherein is'set forth the subject matter of monoand di substitutedcarbodiimide, derivatives of carbodiimide, and the phenyl, tolyl and Xylil substituted products'of carbodiimide, and derivatives theree of, filed co-pending with 399,979.

Divisions of 647,765 already issued are 1,559,-

196; 1,559,197; 1,559,198; and parts still pending are Ser. Nos. 58,469 and 59,726 that relateto the tolyl derivatives.

. The action of organic, nitrogenous, compounds in aiding the vulcanization of rubber is of such a complex character and explained by such va-' ried theories of acceleration that one hesitates to accept any of these theories as correct, but the results of an accelerated vulcanizatiom'or a suitable cutting down of the time and temperature employed in effecting it, is most important, and whether the theory is right or wrong if the result proves of worth, then the art is benefitted thereby and the error-in theory is easily overlooked.

- This situation in the art then is productive of numerous expedients, and many ways of using organic, nitrogenous, bodies to aid and accelerate rubber vulcanization.

This invention makes use of two separate series of substituted guanidines, that respectively are ogou-sly substituted carbodiimides set forth in 647,765 constitute the main components from which the corresponding substituted guanidines of these two series are derived, as well as all their combinations.

Undoubtedly the decomposition products formed from the accelerator during vulcanization, play a most important part.

Triphenylguanidine (C'19E17N3) has been known for a long time as an accelerator, but the re sults, obtained from the use of it are not equal 1 to that of many other accelerators that are just as available for use, and while it has over 14% of nitrogen it still fails to rate with the best of them. Its melting point too is higher than it should be for marked activity in vulcanization.

In a previous patent application, filed by me on July 39, 1920, I mention monophenylguaniadine (C7H9N3) as a rubber accelerator, having a nitrogen content of 31%. v

Here then were two nitrogenous, organic bodies, more or less related in their chemical structure, and an examination of their properties and de composition products showed that the most'natural and logical thing to do would, be-to combine them, and find properties present then, that were more conducive toeffecting a marked accelera tion'in vulcanization than were found when either was usedalone. l Monophenylguanidine' has a melting point of 66 (Qt-and a nitrogen content of 31%, while the melting point of triphenylguanidine is 143- 0. and the nitrogen content 14.6%. The former is quite hygroscopic and soluble in water. The lat ter is practically non-hygroscopic and only slightly soluble in water.

Triphenylguanidine, while it does not decom pose at as-low a temperature as the monophenyl' .guanidine, nevertheless decomposes readily at vulcanizing temperatures and splits off aniline, with its main decomposition product as carbodiphenylimide or its equivalent (diphenylcyanamide, ,CiaHmNz), also of very low melting point and readily polymerizable to a much higher M. P.

Carbomonophenylimide and carbodiphenyl-- llllllde are both of them very reactive bodies and especially so in the presence of the other decomposition products'that' are naturally present with them;

They will combine with each other in more than one molecular proportion, each will combine with either aniline or ammonia, and either will comblue with morethan one phenyl'guanidine.

Both carbomonophenylimide and carbodiphe nylimide form polymerization products which also are more or less reactive with the same bodies as their lower polymers.

The aniline and ammonia released with these two oarbophenylimides is also reactive with more than one of the phenylguanidines.

In the reactions then that follow, from a combination of monophenylguanidine and triphenylguanidine under vulcanization, and with a metallic oxide present, the result would appear to be largely as follows:

Decomposition of the monophenylguanidine into carbomonophenylimide and ammonia.

Decomposition of the triphenylguanidine into carbodiphenylimide and aniline.

Combination of carbodiphenylimide with the nascent ammonia to diphenylguanidine, and probable combination of some of the carbomonophenylimide and nascent aniline to diphenylguanidine.

Nascent diphenylguanidine (supposedly far more active than free diphenylguanidine) might largely be the first product formed, though substantially only as an intermediate product, but subject to the same general trend of decomposition as any diphenylguanidine.

This normal decomposition of diphenylguanidine is authoritatively agreed upon as: First splitting up into carbomonophenylimide and aniline, and then carbodiphenylimide and ammonia being formed.

The carbomonophenylimide first released probably unites gradually with the aniline to produce carbodiphenylimide, just as monophenylurea unites with aniline to produce diphenylurea (Weith, Ber. 9, 821), though the formation of the carbodiphenylimide is explained by early authorities as an entirely separate decomposition.

Recombination of some of the carbo-phenylimides with the nascent aniline, and with the nascent ammonia,may again produce guanidines, but these in turn would decompose again until the gradual combination of the carbo-phenylimides with each other, would slowly eliminate them, and the dissipation of the aniline and ammonia would more rapidly eliminate them and the products that remain then would appear to be largely, unchanged phenylguanidine, uncombined carbo-phenylimides, and the carbo-phenylimide combination products, substantially tetraphenylmelamine, that possesses a melting point above the products started with and of considerable stability.

In vulcanization then, this would indicate an early activity of the accelerator composed of monophenylguanidine and triphenylguanidine While the numerous reactions were taking place and aniline and ammonia were being released, then a reaction stage where the carbo-phenylimides were forming new products, and then an ultimate stage where the progressive reactions were accumulating the higher melting bodies in place of the lower melting bodies started with.

These stages of reaction however are not to be understood as distinctly separate but are periods where the stated reactions predominate. Such an accelerated vulcanization would appear then to promise less activity of the vulcanizing constituents of the rubber after vulcanization than is found with accelerators that decompose into lower melting bodies and generally of lessstability.

That is, in the first case the vulcanized rubber has better aging qualities, or stands aging better, than in the second case.

Much difference of opinion exists as to what these ultimate bodies really are, for varying temperatures of vulcanization and difierent vapor pressures to which a vulcanization may be subjected may somewhat change the order of decomposition of the monoand tri-phenylguanidines and also change the speed of dissipation of the aniline or the ammonia, or even change the order of recombination of these products, but all of these reactions take place substantially between but four important constituents, namely: carbomonophenylimide, carbodiphenylimide, aniline and ammonia.

It is plainly evident then that largely the same end will be attained in any of these reactions, and that variations in temperature and pressure must influence more the degree of such ultimate conversion than it does the production of compounds other than would normally occur, and that ultimately tetraphenylmelamine (tetraphenyltricarbodiimide C2'1I-I22Ns) progressively constitutes apparently a substantial part.

This body has a M. P. of 217 C., is very stable at temperatures below its melting point and appears to be very inactive when not combined with its other related bodies, and in substituting the accelerators started with, because of this high melting point, greatly inhibits further vulcanization in the cold, that is allows the rubber to stand aging better.

An illustration of the formation of tetraphenylmelamine is 2 molecules of carbomonophenylimide and 1 molecule of carbodiphenylimide. (Ann. 1850, 74, 6; Ber. 1874, 7, 1736; Ber. 1875, 8, 912; Monatsh.-1877, 403; Ber. 1887, 20, 1065.)

However, a single molecule of each may react .to triphenyldicarbimide (Czol-IieNi) (M. P. 7074 C.) (Ber. 1887, 20, 1065); but with an excess of carbomonophenylimide present later, the triphenyldicarbimide may readily revert to tetraphenylmelamine.

Should diphenylguanidine (C13H13N3) form in the reactions as an intermediate reaction, as by a combination of the carbomonophenylimide and aniline, or a combination of the carbodiphenylimide and ammonia, or of the triphenylguanidine and ammonia, then the oarbomonophenylimide, or its equalent (phenylcyanamide) may combine with the diphenylguanidine to form triphenylbiguanide (C20H19N5, Ber. 1890, 23, 1668), and Scott claims carbodiphenylimide and the diphenylguanidine can combine to form tetraphenylbiguan'ide (C2sI-I23N5, J. I. E. C. 1923, 15, 286) Triphenylbiguanide has a M. P. of 137 C., and tetraphenylbiguanide has a M. P. of 136 C.

However, since the presence of metallic oxides in vulcanization cause decomposition of an organic accelerator at temperatures much lower than would normally cause it to decompose, and as diphenylguanidine melting at 147 C. must itself first be decomposed to some extent to furnish the necessary constituents for a combination of the carbo-phenylimides with the diphenylguanidine to produce the biguanides mentioned, and as these two biguanides have melting points even lower than the diphenylguanidine, then this same vulcanizing temperature that might be'responsible for their formation cannot fail to largely break them up again, substantially as fast as they may form.

These phenylbiguanides under vulcanizing temperatures and conditions readily release their tetraqsnenylinelamine. 7. r

2: molecules: or carbomonophenyl-imide warms merino or carbophenylimide; and their the diphenylguamidizne mama gives u i-fi-rst'its element therregular way. If the triphenylhi uanine should split oii ammonia instead,-- it waiter merely leave: triphenyrdicarbimide:that mum than sconirevert to tetraphenyl melami ne;

If the tetraphenylbigi'i ani'de should split off aniline instead it: would merely leave triphenyldicairbimicle turn would soon become the tetraphenylbiguanide would resul tin tetrapnenmineiamine direct;- v

' In: a like triphenylizl icarbimide (M; P. 61-) f if present at: any time; is either quick-1y decompose'ct, or forms arr additiorr product with another molecule of carbomonophenyliinideg and this results rtetraphenylnieiaminei I the event that the presenceof ,moi'stu re in these reactions should cause a molecule oiiwator to erate with the carbo -phenylimides to" form corresponding pill-2nylureas, these may to asubextentrecornbihe: again with the nascent aniline, or with the nascent ammonia; splitting otr water; their follow'the" same' norpath: asthe rest, namely to tetraphenyl- I I Many of these reactions are reversible, and the: temperatures that cause the combinations also cause in turn again their separation-. apparent then that triphenyl'dicarbi'mi'de,

km t l bcgua" hide} and tet raphenylbiguanid'e, if.

tetraphenyl rnelamine which isnot so to" these: reverse reactions or to so to each other;

resy a decomposition They may delay the re action; or re fuce the amount: of end product but prevent its being-formed Y should-these guanidi-nes or their disas'sociaproducts, during vulcanization, iorm combinations with the sulphur, or with any of the other usual compounding constituents,-i-t would to largely as catalysts, and rejuvenation; or any of them,- or oi any of their decomlater, would permit the normal reactions to continue That reactions do commie authoritative support, as well as being observable in general practice 0stromuisiensky; Jonr. Russ. Phys; chem- Soot, 4'7, 1e92-3,

igiay; v o or V Monophenyrguanieme and tripheriyl g'uanidine themselves do appear tobe at all antagonistic Their decomposition products too would seem from the foregoing reactions, to not-be antag-- to each other but rather as very suit see toefiect'an accelerated vulcanization during their greatest chemical activity, and then be followed by a quiescence when vulcanization is about-completedor at'an end. Varying the percents'of the twophenyl-guanidines employed,- of course causes a variation in the quantity of the respective carbo-phenyl iir'iidesliberated', which in turn ,woulclprobably govern to a considerable extent the production of the high'melting resultant body that would 7 and between the" twox'ylil substitutd'guanidines very high in a suitable accelerator.

homologous to these twophenylatear guanid-ines.

While aniline enters into tneprcduction of the pnenyl-guanidines mentioned, andis also a decomposition product oi them as well, in: a" like manner" the homologuesof anilinenamely tolui dine and x-yl i dinebea'r a similar" relationto the corresponding tol yl and xylil-guanidinesre'spec-- timely; and are as frequently present with them.

a mono-substituted-guanidine and a tri-substitnted-guanidine; each of which might contain a different homologous radical. I

-. Stich combinations might be especially desirable, so: that a low melting, mono-substitutedguanidine could; bring down the M. P'. of a high melting tri-substi-tuted-guanidine or vice. versa, as a mixture, or in the form of a solid solution,

and" thus allow both to accelerate vulcanization In my investigation of that series of compounds,- of which the severalexam-ples have been mentioned, I havefound that-such mixturesof mone substituted-guanidine and unsubstituted guanidine, or of their decomposition products,

do prove of unusual val u'e inacceleratin'g rubber vulcanization.- r I 'Monophenylguanidine is readily made by"d'e'- sul phurizing: monophenylthiureain the presence 01 ammonialBer. 1879, 12, 1602-), I i It is also made by combining carbophenylimide and ammonia (Beilstein, 1883, II, 920) Another way of producing it is from oyanamide (carbodiimide) and aniline hydrochloride (Am.

Chem. Jnl. 190-1, 26; 2'21; Berg 1904, 37,1681;

Richter, 1922', II, 104) Monophenylg-uanidine is also a decomposition product of 12, '17) r The most convenient Way to make 'triphenylguani'd ine is to desulphurize odi'phenylthiurea;

phenylbiguanid'e (Monatsh. 1891', I

fithiocarbanilide) with litharge in the presence 1 A combination then of" these two phenyl-guanidines may be readily effected and in several ways. One manner of preparing this miX'ed f phenyl guanidine accelerator is to use molecular proportions, and take twice the molecular proportion of the lower melting or'mono-phenylguanidine, and one: molecular proportion of the highermelting or triphenylguanidine. 4

Reduced to specific quantities the proportions would be, about 15 lbs. of monophenylguanidine and 1 6 lbs. o'l triphenylguanidine."

The nitrogen content of the 7 mixture then would be a little above-25% which would be rated Should molecular proportion of the monoand tri-phenylguanidines be used; theoretically no aniline or ammonia would be left over and an eqtia'l- Weight'of nascent diphenylguanidine would theoretically result as the first combination prodnote 02 the disassociation- The nitrogen content would then-be over l9 v As a large quantity of the'low IIIIfiIig- IIIOIIO- phenylguanidine (66 0.) might lower the M. P. of the combined product to such an extent as to possibly interfere with its usefulness, a less amount of itmight be preferable. This quantity change however could not materially affect the general trend of the decomposition, for instead of any reaction consuming carbomonophenylimide in conjunction with aniline to produce carbodiphenylimide, the carbomonophenylimide could combine direct with the carbodiphenylimide from the triphenylguanidine.

The less amount of ammonia split off in the disassociation of the monophenylguanidine then, would merely lessen the quantity of intermediate diphenylguanidine, formed (from combination with carbodiphenylimide), but not substantially affect the combination of the carbo-phenylimides with each other. 7 7

Even an excess of carbodiphenylimide could combine with such nascent ammonia as there was, to form diphenylguanidine, then emerge from the diphenylguanidine, under decomposition, as carbomonophenylimide, and so readily aid in readjusting the reactions to a suitable equilibrium again so that the path of normal decomposition could be largely followed.

In combining these two phenylguanidines, a mechanical mixture of them well stirred together before use would seem to be the simplest way to utilize them.

However, they may be melted together by heat, or found together with their by-products or decomposition products, due to manufacture, or the decomposition products of one may be added to the other or to the decomposition products of the other, or either may be added separately to the rubber mix, or the decomposition products of either may be added separately to the rubber mix.

Any of these means, or any other means for effecting a combined activity of these two phenylguanidines themselves, or of their decomposition products, or the introduction into a vulcanization of the carbo-phenylimides (as easy to obtain or to make as these guanidines) either with or without aniline or the ammonia, or the presence of any products that would supply them in a manner to effect a similar reaction activity, or that would ultimately result in tetra-substitutedmelamine as the end product, is intended to be covered by this specification.

Whilethe above proportions may seem to be the most desirable, yet the proportions may be changed considerable to meet thevarious vulcanizing conditions.

These combinations of monophenylguanidine and triphenylguanidine, or mixtures of their equivalents as accelerators, appear then to derive much of their eificiency from thepeculiar circumstance that the disassociation inter-reactions of the two guanidines cause the gradual formation, within the heated rubber, of nascent diphenylguanidine as an intermediate.

This intermediate diphenylguanidine forms then while the disassociation end products are also forming,'and the intermediate or nascent diphenylguanidine is capable of great activity, as it breaks up however, it follows the usual disassociation course that leads to ultimate tetraphenylmelamine.

Combinations of monoand tri-substituted guanidines, homologous to these phenyl sub stituted guanidines, show much the same reaction behavior under vulcanizing temperatures.

My invention then consists in making use of these two substituted guanidines in a new man,- ner, that initiates quite new and different reactions between them during rubber vulcanization, and that greatly accelerates the vulcanization of the rubber in which they areemployed, and also gives resultant products thatare highly improved from their use.

It is to be understood that I do not limit myself to the ingredients, components and proportions, given in this specification, or. to, such examples-as have been cited by me, it being readily understood by those well versed in the art, that said ingredients, components and proportions may be varied within comparatively wide limits without departing from the principles and purposes of my invention as herein set forth.

It is further to be understood that my inven-, tion is not to be construed as dependent on the accuracy or soundness, of any of the theories herein expressed. g

Having now described my invention and having shownin what manner the samemay be utilized, what I claim as new, and desire to secure by Letters Patent is:

1. A process of vulcanizing rubber which consists in, incorporating into rubber an accelerator comprising the combination of monophenyl: guanidineand triphenylguanidine, then heating the resultant rubber mixture with a vulcanizing agent to effect vulcanization.

2. A process ofvulcanizing rubber whichconsists in, incorporating into rubber-an accelerator comprising the combination of a mono-substi-. tuted-guanidine with. a tri-substituted-guanidine, then heating the resultant rubber mixture with a vulcanizing agent to effect vulcanization.

3. A process of vulcanizingrubber which conmono-substituted guanidine, a tri-substituted guanidine, and ammonia, then heating'the'resultant rubber mixture with a vulcanizing agent to effect vulcanization. I r

4. A process of vulcanizing rubber whichconsists in, incorporating into rubberan accelerator comprising the combination of a mono-substituted-guanidine, a tri-substituted-guanidine, and aniline or one of its homologues, then heating the resultant rubber mixture with'a vulcanizing agent to effect vulcanization. Y

5. A process of vulcanizing rubber which consists in, incorporating into rubber an accelerator comprising a combination of a mono-substitutedguanidine, a tri-substituted-guanidine, aniline or one of its homologues, and ammonia, then heating the resultant rubber mixture'with' a Vulcanizing agent to effect vulcanization.

6. Aprocess of vulcanizing rubber which consists in, incorporating a vulcanizing agent with rubber, then applying heat and effecting an accelerated vulcanization through the presence of monophenylguanidine and triphenylguanidine in the rubber mixture. 7

7. A process of vulcanizing rubber which consists in, incorporating a vulcanizing agent with rubber, then applying heat and effecting an accelerated vulcanization through the presence of a mono-substituted-guanidine and a tri-substituted-gu'anidine in the rubber mixture.

8. A process of vulcanizing rubber which consists in, incorporating a vulcanizing agent'with rubber, then applying heatand effecting an accelerated vulcanization through the presence of a mono-substituted-guanidine, a tri-substituted guanidine and aniline or one of its homologues in the rubber mixture. I

9. A process of vulcanizing rubber which consists in, incorporating a vulcanizing agent with compounded rubber, then applying heat and efiecting an accelerated vulcanization through the presence of a mono-substituted guanidine, a tri-substituted guanidine, and ammonia, in the rubber mixture. V

10. A process of vulcanizing rubber which consists in incorporating a vulcanizing agent with rubber, then applying heat and effecting an accelerated vulcanization through the presence of a mono-substituted-guanidine, a tri-substitutedguanidine, aniline or one of its homologues, and ammonia in the rubber mixture.

11. A process of vulcanizing rubber which con sists in, incorporating with compounded rubber a vulcanizing agent, and mono-phenylguanidine and tri-phenylguanidine as an aid to vulcanization, then under heat inducing a decomposition of the two phenyl-guanidines in the rubber mixture, while efiecting anaccelerated vulcanization.

12. A vulcanized compound derived from, compounded rubber or similar material combined with a vulcanizing agent and an accelerator comprising monophenylguanidine and triphenylguani'dine. c g V I 13. A vulcanized compound derived fr0m,*compounded rubber or similar material combined with 'a vulcanizing agent and an accelerator comprisingmono-substituted guanidine and tri-substituted guanidine.

14;. A vulcanized compound derived from, compounded rubber or similar material combined with a vulcanizing agent and an accelerator comprising mono-substituted guanidine, tri-substituted guanidine, and aniline or one of its homologues. i y a J 15. Avulcanized compound derived from, compounded rubber, or similar material combined with a vulcanizing agent and an accelerator comprising mono-substituted guanidine, tri-substituted guanidine, ammonia, and aniline or one of its homologues. v I

GEORGE H. STEVENS. 

